Field of the Invention
The present invention relates to a photoacoustic image generation apparatus, system and method, and particularly to a photoacoustic image generation apparatus, system and method in which light is output to a subject to be examined, and an acoustic wave induced in the subject to be examined by illumination with the light is detected, and a photoacoustic image is generated.
Description of the Related Art
Ultrasonography is known as one of image examination methods that can perform non-invasive examination to find the state of the inside of a living body. In ultrasonography, an ultrasonic probe that can send and receive ultrasound is used. When ultrasound is sent from the ultrasonic probe to the subject to be examined (living body), the ultrasound travels in the living body and is reflected at a tissue interface in the living body. The reflected ultrasound is received by the ultrasonic probe. It is possible to image the state of the inside of the subject to be examined by calculating a distance based on time till the reflected ultrasound returns to the ultrasonic probe.
Further, photoacoustic imaging, which images the inside of a living body by utilizing photoacoustic effects, is known. Generally, pulsed laser light is output to the inside of the living body in photoacoustic imaging. In the inside of the living body, living tissue absorbs energy of the pulsed laser light, and ultrasound (photoacoustic signals) is induced by adiabatic expansion caused by the energy. The photoacoustic signals are detected by an ultrasonic probe or the like, and a photoacoustic image is constructed based on the detection signals. Accordingly, it is possible to visualize the inside of the living body based on the photoacoustic signals.
Meanwhile, in ultrasonic imaging, harmonic imaging is known. In harmonic imaging, the frequency of ultrasound sent into the subject to be examined is regarded as a fundamental frequency, and ultrasound with frequency of an integer multiple of the fundamental frequency (harmonics) is detected. Further, an ultrasonic image is generated based on the detected harmonics. Regarding harmonic imaging, Japanese Unexamined Patent Publication No. 2004-073620 (Patent Document 1) discloses generation of a fundamental frequency image based on a fundamental frequency, and generation of a harmonic image based on harmonics, and display of the fundamental frequency image and the harmonic image that are combined together by addition. Further, Japanese Unexamined Patent Publication No. 11 (1999)-290318 (Patent Document 2) discloses the feature that a fundamental frequency image and a harmonic image are partially combined together so that a region of interest is composed of a harmonic image and the other region is composed of a fundamental frequency image.